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I am currently building an Arion Lightning, which has a fiberglass fuselage with a stainless steel firewall. I will be paying attention to making penetrations fire resistant (e.g. not using plastic or aluminum pass-throughs), but I am wondering about the mounting of the firewall directly against the fiberglass fuselage flange. It would seem that the heat of a fire, applied to the fiberglass via the thin stainless sheet, would quickly cause a lot of smoke and failure as the fiberglass overheats and burns. I was reading about this on Van's forum, and looking at recommendations from (I think it was Dan Horton??) who did a lot of research and favored use of a high temperature insulation (like 1/8" of fiberfrax), covered with a thin (0.002") stainless layer to protect the fiberfrax, both on the engine side of the firewall. This would seem even more critical on a fibrerglass aircraft than on a aluminum aircraft. So, I was wondering what other fiberglass aircraft use in this area, or what other fiberglass aircraft builders are doing, if anything, to enhance fire resistance of the firewall?

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You could also try having the stainless firewall on small standoffs to keep it from contact with the composite material. Seal any feedthroughs with PR812 sealant or BMS 5-63 as you are in Boeing country.

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Yes, as I understand it, the underfloor is another critical area becase the flames are initially swept against that area by the cowling exhaust air. This is also often a big weakness in aluminum aircraft -- even though the SS firewall may hold, the aluminum on the belly can melt away very quickly and then the fire consumes your feet as you try to get down. Aesthetically, it's harder to protect that area, since it's visible and it has compound curves that stainless sheet is hard to form around, and it's not pretty if you try. I have located a few moderately high temperature (~1200F/649C) insulating materials that have some "formability", but these are mostly aluminum faced insulation, which limits their usefulness. (They are generally made to reflect exhaust heat from nearby exhaust parts, not made as a fire-retardant material). Still, they may slow things down a little to buy time, as Nev says. I am thinking of using the aluminum stuff on the rear inside of the cowl to try to kept the cowl intact awhile and containing the flame, and maybe a small SS deflector under the cowl outlet just to keep the flames from making direct impingement on the belly skin, if I can convince myself that it would work. (might loose a couple knots on that).

I would love to find some deeply "dimpled" thin stainless sheet, as dimples tend to allow the material to take compound bends, but I don't see any suppliers.

I also like the idea of standoffs for the firewall, but these would obviously still need to be sealed. I looked up those sealants-- 400F (204C) service temperature and "flash" temps as high as 2000F for one and the other at 3500F (1925C) !!!! Great stuff but also PRICEY at $200-400 US for a small tube!!

Thanks for the thoughts -- keep them coming.

Ted

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All types of fibreglass will burn, but worse than this, all resins lose their structural integrity as they heat up. As Nev suggests, anything that postpones this can save your life. Don't underestimate the value of wood as a fire insulator. A SS-lined plywood firewall is easy to integrate into a composite aircraft and will keep its shape far longer than fibreglass resin, which will quickly turn to slop.

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Interesting that nobody yet has said, "don't worry about it, just build it and go fly".

Wood is an interesting thought. I'll have to look into what temperature it starts to char vs Fiberglass turning to "slop". Another advantage is that if it didn't delay the fire long enough, you would die to the pleasant smell of a campfire rather than toxic resin fumes. ;)

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All types of fibreglass will burn, but worse than this, all resins lose their structural integrity as they heat up. As Nev suggests, anything that postpones this can save your life. Don't underestimate the value of wood as a fire insulator. A SS-lined plywood firewall is easy to integrate into a composite aircraft and will keep its shape far longer than fibreglass resin, which will quickly turn to slop.

You can look at the properties of fire retardant resin. There is a photo somewhere of a Shell gas tanker in England on fire after a crash, where the FRP tanker, constructed using fire-retardant resin was squashed and then rebounded to its shape with a large hole in the corner the spilled gasoline caught fire , but can be seen bubbling from boiling, still contained in the FRP.

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M61A1: Thanks for the link. That link suggests using the same material as I have purchased to insulate my firewall, but thinner stainless steel, and no overcover for the Fiberfrax, because it says to put the Fiberfrax between the firewall and the composite. (I was planning to put the stainless steel firewall directly on the composite flange per the plans, but then overlay with Fiberfrax and very thin stainless sheet (0.003 inch) to protect the Fiberfrax. That is, the insulation on the engine side vs the cockpit side of the stainless firewall. However, I think the link might be describing installation on a full composite bulkhead, vs a flange. In my case, I think cockpit side material would compress too much between the flange and the firewall (loosing insulation effectiveness) especially since the motor mounts go on top of the firewall, compressed against the flange with four AN7 bolts.

I can also get save a few pounds compared to the uninsulated kit material weight if I use .018 inch stainless steel instead of the 0.030 supplied with the kit. I called the kit manufacturer, and he confirmed the kit does not require the thicker stainless for any structural reason. But no information on fire-resistance improvement of sides and bottom of the fuselage. Guess I'm still on my own for that.

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Dave:. I did about 7 days of build assist. I wanted to get major structures done and the canopy, then trailered it back home. I'm surprised you don't have yours yet -- hope it's worth the wait. My fuselage arrived a little late, and (long story) I ended up with an epoxy fuselage instead of vinyl ester. Anyway, Nick (for others, Nick is the Arion Aircraft owner) worked with me over Saturday to catch up the lost time. I've never posted pictures on this forum, but I'll add a couple once I figure it out.

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Suitable heat insulation will also act as sound deadening. I don't know what engine you are using but any oil tank or cooler holds oil that burns extremely well. If you fly at heights rather than low you will take longer to get down if you are alight. Consider underfloor as well. and cowl gills /flaps to seal it up and reduce the oxygen available (and increase cruise speed).. . Heat shield and safety all oil and fuel lines. Nev

FWIW: My engine is a Titan 340 (experimental) with vertical induction, Airflow Performance fuel injection, and twin E-mag electronic ignition. I went with low compression pistons since I don't trust the future fuel options. I will be using a Prince fixed pitch prop. Great props and built locally. I can literally ride my bicycle to Prince Propellers.

The Arion Lightning was really designed originally for a Jabiru 3300, and perhaps I should have stuck with it (the kit is more complete if that option is used, and there is a lot to be said for the Jab. However, market penetration in the US is much stronger with Lycoming clones, and of course I have more horsepower with this option.

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If I was building an aircraft (but I'm not), I would be paying attention to shielding of high temperature areas, location and protection of potential fire sources, such as oil and fuel hoses, and ensuring that every feature of the cabin interior design was as fire-resistant as possible.

In addition, I'd be paying attention to ensuring cabin exit ability after a crash is easy, and there can be no confusion with regard to door or canopy latches.

There are two major scenarios that obviously worry most pilots in the back of their mind - smoke, then flames, in the cockpit - and being trapped in an aircraft that is on fire.

As a large majority of aircraft end up inverted after a crash, one has to remember that confusion is the primary problem when inverted, everything is upside down, and you lose precious seconds trying to re-establish your orientation.

I understand the commercial aircraft designers go to great lengths to ensure any fire activity on aircraft is slowed down at every possible point, thus enabling people to gain additional time to calculate their options and ways out.

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When I was building my SK Jabiru, I thought that the weight of the galvanized iron sheet firewall was excessive. Fibrefax and thin stainless would have been better over the plywood bulkhead and I wish I'd done that. Mind you, the 3M silicon stuff looks good too and might have been lighter again, but how would you know you had applied it properly?

But one thing about tractor engines, they are better for fire. Much better than having the engine behind you.